Staphylococci are a type of indigenous bacteria in humans, and are also known to cause infections. For example, Staphylococcus aureus is said to be carried by 20-30% of people persistently, and by 50-60% of people transiently (Non-Patent Document 1). Other than in food poisoning, skin/soft tissue infections (such as impetigo and cellulitis) and the like, the bacteria are usually almost non-virulent to healthy individuals. However, they often cause serious infections in people such as patients who underwent highly invasive surgery, hemodialysis patients, patients who received bio-replacement with artificial medical devices, diabetic patients, and extremely premature infants whose immune systems are immature and in whom indigenous bacterial flora have not been formed.
The development of anti-microbial agents for staphylococci started with the β-lactam penicillin. However, staphylococci easily acquired a drug-resistance mechanism genetically, and resistant bacteria appeared a few years after penicillin went on sale. Various antimicrobial agents, such as aminoglycoside, macrolide, chloramphenicol, tetracycline, quinolone, and penem antimicrobial agents were subsequently developed, but were not able to overcome resistant bacteria. Additionally, bacteria resistant to vancomycin, a glycopeptide antimicrobial agent which did not have resistant bacteria for a long time after development, eventually appeared (Non-Patent Document 2). Furthermore, an oxazolidine antimicrobial agent, which was developed recently as the first novel antimicrobial agent in a few decades, was found to have resistant bacteria thereto the year it went on sale (Non-Patent Document 3).
As described above, multidrug-resistant staphylococci exhibiting resistance to most antimicrobial agents have emerged, and among them, Staphylococcus aureus, as the main pathogen of nosocomial infections, especially, imposes a great threat. In fact, it is estimated that the number of patients invasively infected by methicillin-resistant Staphylococcus aureus (MRSA) comes up to 94,000 in the USA annually, of whom, an estimated 18,000 die (Non-Patent Document 4). Moreover, with advanced medical care becoming available in countries outside of medically advanced countries, the chance and risk of contracting Staphylococcus aureus infections have become higher, and patients suffering from Staphylococcus aureus infections are predicted to increase in the future. Furthermore, cases of highly virulent community-acquired MRSA infections, where healthy individuals contract the infections in communities and exhibit severe symptoms, (Non-Patent Document 5) are also increasing.
Accordingly, new therapeutic strategies different from the conventional treatments with antimicrobial substances are strongly desired, and recently, studies have been carried out on infection protection using vaccines or antibodies. Examples of the vaccines include Staphylococcus aureus capsular polysaccharide types 5 and 8, and iron surface determinant B; and examples of the antibodies include antibodies for clumping factor A, ABC transporter, or teichoic acid.
Additionally, the disclosures of the following non-patent documents are all incorporated herein by reference.    Non-Patent Document 1: Rebecca A. Brady, Jeff G. Leid, Anne K. Camper, J. William Costerton, and Mark E. Shirtliff (2006) Infect. Immun. 74: 3415-3426.    Non-Patent Document 2: CDC (2002) MMWR 51: 565-567.    Non-Patent Document 3: Sotirios Tsiodras, Howard S. Gold, George Sakoulas, George M. Eliopoulos, Christine Wennersten, Lata Venkataraman, Robert C. Moellering Jr, and Mary Jane Ferraro (2001) Lancet 358: 207-208.    Non-Patent Document 4: R. Monina Klevens, Melissa A. Morrison, Joelle Nadle, Susan Petit, Ken Gershman, Susan Ray, Lee H. Harrison, Ruth Lynfield, Ghinwa Dumyati, John M. Townes, Allen S. Craig, Elizabeth R. Zell, Gregory E. Fosheim, Linda K. McDougal, Roberta B. Carey, and Scott K. Fridkin (2007) JAMA 298: 1763-1771.    Non-Patent Document 5: CDC. (1999) MMWR 48: 707-710.    Non-Patent Document 6: Adam C. Schaffer and Jean C. Lee (2009) Infect. Dis. Clin. North. Am. 23: 153-171.